Stack light



FIG. 1 is an top, front perspective view of a stack light showing our new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof; and,

FIG. 5 is a right side elevation view thereof.

The dot-dash broken lines represent the bounds of the claim and form no part of the claimed design. The appearance of any portion of the article within the area defined by the dot-dash broken line in FIG. 1 likewise forms no part of the claimed design. 

CLAIM The ornamental design for a stack light, as shown and described. 